There are some things you should know about Harriet Wermer. She used to lie a lot, but not anymore. Seriously, she only tells the truth now. Even though she hadn't wanted to come to Marble Island in the first place, now she doesn't want to leave. It's the truth. With her mom and new baby brother home from the hospital, it's almost time for Harriet to pack up and head home from Marble Island and all the friends she's made. But Harriet doesn't have time to think about that--not when she discovers that Moneypenny, her Nanu's adorable basset hound, has been poisoned.